In chemistry, the molecule is the smallest indivisible portion of a pure compound that retains a set of unique chemical and physical properties. A molecule consists of two or more atomsbonded together.

Figure 1, 3D (left and center) and 2D (right) representations of the terpenoid, atisane[?]. In the 3D model on the left, carbon atoms are represented by gray spheres, white spheres represent the hydrogen atoms and the cylinders represent the bonds. The model is enveloped in a "mesh" representation of the molecular surface, colored by areas of positive (red) and negative (blue) charge. In the 3D model (center), the light-blue spheres represent carbon atoms, the white spheres are hydrogen atoms, and the cylinders in between the atoms correspond to single-bonds.

Most molecules are much too small to be seen with the naked eye, but there are exceptions. A grain of salt, or the diamond on an engagement ring, are giant crystal lattices, repetitive molecules with atomic bonding (usually ionic bonding) connecting the entire structure.